The present invention relates to multilayer medical working means, such as flexible tubes, containers, molded parts, etc., having at least two walls made of a glass-clear, soft plastic, one of the walls being toxicologically unobjectionable and the other wall or walls being provided with additives. A full-area circumferential connection exists between each of the walls.
In the medical field, standards exist which govern whether it is permissable to use a particular plastic in a medical working means. An example of such a standard is German Industrial Standard DIN 58,361, entitled "Transfusionsbehaltnisse und Zubehor", in translation, Transfusion Vessels and Accessories". In Europe, the draft PA/PH/Exp. 3/T (80) 3 of the European Pharmacopoeia Commission corresponds to this standard. It provides that technical working means made of plastic are permissible in the medical field, inter alia, only if they are toxicologically unobjectionable and contain neither antioxidants nor coloring agents.
In this connection, the use of softened polyvinyl chloride containing the softener di-(2-ethyl hexyl)-phthalate (DOP) is permissible.
To meet the high demands placed on the use of plastics for the manufacture of medical working means, processes have become known which are intended to prevent the toxicological effect of a certain plastic, which plastic appears to be particularly suitable for the intended type of use, by coating it with other toxicologically unobjectionable plastics. For example, German Pat. No. 1,930,136 discloses a coated catheter which is basically a tube made of rubber or some other elastomer which is provided with a coating of a hydrophilic acrylate or methacrylate, respectively.
After the catheter has begun to swell, the acrylate or methacrylate layer is polymerized to form a solid coating. Antibiotic or germicidal substances can be applied to this layer which are then retained by the hydrophilic coating. Thus, the catheter is made more patient compatible in situ.
Finally, U.S. Pat. No. 3,618,614 discloses a medical tubing comprising a relatively thick, transparent inner tube and a relatively thin, transparent outer tube, each made of plastic. The outer tube is provided with a radiopaque material so that the path of the tube within the patient can be observed on the X-ray screen. The tubing combination disclosed in this patent comprises, for example, an inner tube of polyethylene with additives such as bismuth oxychloride and ethyl-2-(3 amino-2,4,6-triiodobenzoyloxy)butanoate, and an outer tube of polyethylene with additives of triiodo and tetraiodo benzoic acid ester which are distributed homogeneously in the walls of the outer tube as the radiopaque material.
Under consideration of DIN No. 58,361, this tube cannot be used as medical tubing because nonpermissible additives were used together with the basic polymers.
The drawbacks of the prior art in the manufacture of toxicologically unobjectionable working means for medical use are that manufacturing processes are employed for this purpose which are complicated and work-intensive. For example, after extrusion of the basic tubing, the toxicologically unobjectionable layers are applied by a further process step such as immersion, spraying or coating in some other way. When softener-containing PVC materials are used to manufacture the tubing, the tendency of the softener to migrate has in the past not been considered and this migration may lead to the tube walls becoming brittle.
In the past, scant consideration has been given in the medical field to technological working means, for example tube systems, for photosensitive solutions. Contrary to the rules set by DIN No. 58,361, interested consumers have made do with the use of tube systems that were dyed black or dark and with accessories which, although they protected the substance flowing through the tubing against the entire wavelength range of visible as well as invisible light, have the drawback, in addition to the fact that they are used contrary to the standard, that the material flowing through them cannot be observed. Possibly occurring bubble formation, dirt particles or other malfunctions, which have a life threatening importance for the patient, for example during infusions, cannot be observed directly with such working means and can therefore not be alleviated as soon as they occur.